There is great demand for high capacity communication links in a variety of industrial and government settings including, for example, in mobile telephony, satellite communications, broadband data communications, etc. Existing methods for increasing the capacity (e.g., the data rate) of a communications link suffer from high costs, high power requirements, and the limited availability of bandwidth. For example, it is known to increase communications link capacity using higher-order modulation techniques such as, for example, 16 QAM. Successfully implementing higher-order modulation techniques, however, requires a relatively high bit energy to noise spectral density ratio (Eb/No) and linear power amplifiers. High values for Eb/No require increased transmission power. Operating a power amplifier in a linear manner, however, often requires an increased power back-off. Accordingly, the use of higher-order modulation techniques is often unsatisfactory. This is especially the case in communications links with severe power constraints, such as, for example, high capacity satellite links. It is also known, for example, in the commercial television industry, that increased communications link capacity can be obtained using power division multiple accessing (PDMA). According to PDMA, two or more signals may occupy the same spectrum bandwidth. At least one of the signals, however, must have a relatively higher power level, typically 10 dB or more depending on the number of signals. Again, power constraints often render these methods undesirable.